The present invention relates to a method for steering a vehicle and a steering system for a vehicle.
In power-assisted steering systems, a torque-supporting hydraulic or electric steering actuator may reduce the torque to be applied for steering the vehicle and thus may relieve the driver. In addition, in power-assisted steering systems, it is believed that the torque support and/or the transmission ratio of the steering system are speed dependent. At lower speeds, such as those typical for parking and unparking, very direct steering having high torque support may be used, while during more rapid travel, indirect steering having low torque support may be desirable.
In order to further increase the driving stability of vehicles, steering systems may include a driving dynamics regulator that adjusts the setting of the steered wheels independently from the steering wish of the driver. In this case, the driving dynamics regulator superimposes an additional steering angle on the steering wish of the driver at the steering column.
In these steering systems, torque support and driving dynamics regulation mutually influence one another, which may result in the following disadvantages:
Due to the low torque support and indirect steering at high driving speeds, interventions in positioning the steered wheels which are performed by a superposition gearbox on the steering wheel motor acting on the steering column may not be performed with the necessary speed.
The torque support and the steering feel, which is transmitted to the driver by the steering wheel, may not be capable of being influenced and adjusted independently of one another.
It may be at least difficult to integrate further functions into the steering system.
An object of an exemplary embodiment according to the present invention is to provide a method for steering a vehicle, in which the torque support and driving dynamics regulation do not negatively influence one another. In addition, an exemplary method according to the present invention may be easily adapted to various vehicle types and may ease the integration of further functions.
This object is achieved by an exemplary method according to the present invention, in which the steering wheel angle is detected, the steering wheel angle is modified as a function of the driving speed, a correction steering angle is determined as a function of the driving dynamics of the steered vehicle, the modified steering wheel angle and the correction steering angle are superimposed to form a setpoint steering angle, the position of the steered wheels is detected, the angle difference between the setpoint steering angle and the position of the steered wheels is formed, the position of the steered wheels is regulated as a function of the angle difference (xcex4Pinion,setpointxe2x88x92xcex4Pinion), and the correction steering wheel angle is compensated for at the steering column.
In an exemplary method according to the present invention, the driving dynamics intervention is not performed by activating the steering wheel motor acting on the steering column, but rather by activating a steering motor acting on the steered wheels. In this manner, the driving dynamics intervention is independent of the torque support of the steering actuator and, in addition, the steering column is relieved from transmitting the torque caused by the driving dynamics intervention.
The steering wheel motor of a steering system operating according to an exemplary method according to the present invention is used for compensating the change in the position of the steered wheels caused by the driving dynamics intervention, so that the steering feel may be influenced independently of the torque support. Therefore, a steering system operating according to the exemplary method according to the present invention may be more easily adaptable and easier to control. In addition, the reliability of the steering system may be increased, since the steering column is relieved in relation to typical power assisted steering systems having a driving dynamics regulation system. This compensation is not restricted to the change in the steering feel, which is caused by the driving dynamics intervention, but may also be used for a change in the steering feel for other reasons.
The position of the steered wheels may be regulated by a first position regulator having PD characteristic or a cascade structure, the output signal of the first position regulator is a setpoint torque to be transmitted from the steering motor to the pinion, the setpoint torque is converted into a setpoint current, and the steering motor is driven with the setpoint current, so that high-quality regulation is ensured.
In addition, further functions may be integrated into an exemplary method according to the present invention without a large outlay. At the same time, a steering system operating according to an exemplary method according to the present invention may remain easily adaptable.
In another exemplary method according to the present invention, the first position regulator has a nonlinear static characteristic or an adaptive variable characteristic, so that the regulation behavior may be further improved.
In a further exemplary method according to the present invention, the modified steering wheel angle (xcex4H+) is converted into a setpoint yaw rate (xcfx89ref) or a setpoint transverse acceleration (ay), and a correction steering wheel angle (xcex94xcex4H,Setpoint) is regulated as a function of the setpoint yaw rate (xcfx89ref) or the setpoint transverse acceleration (av), so that the driving stability of the vehicle is further increased by influencing the position of the steered wheels. The output signal of the yaw regulator is a correction steering wheel angle (xcex94xcex4H, Setpoint), which may be superimposed on the reference variable of the first position regulator and in addition may be used as a reference variable at the steering column for compensating the steering movement.
In yet another exemplary method according to the present invention, the yaw regulator is a PD regulator or a model-following regulator, so that stable regulation behavior of high regulating quality may be achieved.
In still another exemplary method according to the present invention, the correction steering wheel angle is converted into a correction torque, the differential torque existing between the two parts of the steering column is measured, the torque difference is formed from the correction torque and the differential torque, and the correction steering wheel angle is compensated for as a function of the torque differential. Through the regulation of the hand torque, the change in the steering feel, which results from an intervention of the driving dynamics regulator in the position of the steered wheels, may be completely compensated for, so that the driver of the vehicle does not feel this intervention.
In yet another exemplary method according to the present invention, the correction steering wheel angle is converted into a correction torque, the correction torque is converted into a setpoint correction current, and the correction steering wheel angle is compensated for at the steering wheel as a function of the setpoint correction current, so that a torque sensor on the steering column may not be required.
In still another exemplary method according to the present invention the rotational angle difference between both parts of the steering column is measured, the angle difference is formed from the correction steering wheel angle and the rotational angle difference, and the correction steering wheel angle is compensated for at the steering wheel as a function of the angle difference, so that an angle sensor may be used on the steering column instead of a torque sensor.
In yet another exemplary method according to the present invention, a lane guidance steering wheel angle change is determined, and a setpoint torque difference is superimposed on the setpoint steering torque as a function of the lane guidance steering wheel angle change and the modified steering wheel angle, so that, without intervening in the structure of the exemplary method according to the present invention, a lane guidance regulation system may be integrated into the exemplary method. In the same way, further functions may be integrated into an exemplary method according to the present invention.
In still another exemplary method according to the present invention, a lane guidance steering wheel angle change is determined, the angle difference is formed from the modified steering wheel angle and the lane guidance steering wheel angle change, a lane guidance steering wheel angle difference is superimposed on the modified steering wheel angle as a function of the angle difference, and the setpoint steering angle is regulated as a function of the setpoint steering wheel angle resulting therefrom, so that the driver feels the intervention by the lane guidance regulator through the change in the torque transmitted to his hands by the steering wheel.
In variants of the integration of the lane guidance regulation system, the driver detects the intervention by the steering feel and he may decide whether he will accept this preset course or not. However, the driver still has the responsibility for the driving direction of the vehicle as before; he may also ignore the course preset by the lane guidance regulator.
The object described above may also be achieved by a steering system for a motor vehicle having a steering wheel mounted on a steering column, having a rotational angle or torque sensor mounted on the steering column, having a steering gearbox, having a hydraulic or electrical steering actuator, having a second rotational angle sensor to measure the position of the steered wheels, and having a control device, a steering motor acting on the steered wheels being present, so that the advantages of an exemplary method according to the present invention may also have an effect in this steering system.